# Attic frost and ice dams in Edmonton homes: causes and fixes By Banish Angural · Published October 18, 2026 > Attic frost and ice dams in Edmonton homes are usually caused by warm, moist air leaking from the house into the attic through gaps around fans, lights, plumbing stacks and the hatch. In long cold spells the moisture freezes on the roof sheathing. Air sealing comes first, then insulation and balanced ventilation, with bathroom fans vented outdoors. After a long Edmonton cold spell, some homeowners find water dripping from a ceiling light or a stain spreading on the drywall, even though it has not rained in weeks. The cause is often attic frost that has built up during the cold and then melted. Ice dams at the eaves are a close cousin, and both start in the same place: warm house air getting into a cold attic. This post explains why it happens, what to look for as a buyer, and what fixes it. If you are buying in winter, our [winter home inspection guide](https://edmontonhomeinspector.com/blog/winter-home-inspection-edmonton) covers what else a cold-weather inspection can and cannot check. ## What causes attic frost? Attic frost forms when warm, moist air from the house leaks into the attic and freezes on the cold underside of the roof. Natural Resources Canada’s [Keeping the Heat In guide](https://natural-resources.canada.ca/energy-efficiency/homes/make-your-home-more-energy-efficient/keeping-the-heat/chapter-5-roofs-and-attics/15637) says air leaks through chimneys, vents, plumbing and electrical boxes can cause substantial heat loss and moisture problems, and that even an insulated attic can benefit from air sealing. Common leak points, according to NRCan: - Bathroom and kitchen fans that pass through the ceiling. - Plumbing stacks and chimney chases. - Wiring holes and pot lights. - The attic hatch, if it is not sealed and insulated. The more moisture there is in the house, the worse it gets. Showers, cooking, laundry, lots of people or plants, and a humidifier set too high all add water to the air that can find its way up. ## Why does it get worse during Edmonton cold snaps? The longer and colder the spell, the more frost builds up, and a sudden warm-up melts it all at once. A [2017 CBC report](https://amp.cbc.ca/lite/story/1.3933782) describes this as attic rain: moist air freezes in the attic during the cold and leaks into the home when it warms up. A later [CBC story](https://www.cbc.ca/news/canada/calgary/attic-rain-calgary-alberta-cold-weather-1.7097529) quotes roofers who tie it to indoor humidity during extended stretches below about minus 15. The [Travelers Canada guide to attic rain](https://www.travelerscanada.ca/resources/home-warranty/managing-attic-rain) explains that this frost can melt quickly and drip through ceilings, vents and light fixtures. That is why the damage often shows up a few days after the cold breaks, not during it. Newer homes are not immune. The 2017 CBC report notes that more airtight, energy-efficient homes can be more prone to it, because a few small gaps let moist air into an attic that otherwise stays very cold. ## Are bathroom fans really a big part of it? Often, yes. A bathroom fan moves a lot of warm, wet air. If its duct is disconnected, crushed, or ends in the attic instead of outside, that moisture goes straight onto the cold roof boards. Things an inspector looks for in the attic, where it is safe to enter: - Fan ducts that are loose, torn or simply end in the insulation. - Ducts that sag and collect condensation, or that are not insulated. - Frost or staining concentrated around a fan, a stack or the hatch. - Exhaust that vents at the soffit, where moist air can be drawn back into the attic. On the living side, a fan that is very loud, very weak, or has no visible outside hood is worth a question. ## What causes ice dams? Ice dams form when heat from the house warms the roof deck, melts snow on the upper roof, and the meltwater refreezes at the colder eaves. The ridge of ice then holds back more water, which can work its way under the shingles. CMHC’s [About Your House pamphlet on attic venting, attic moisture and ice dams](https://publications.gc.ca/site/eng/9.615641/publication.html) links ice dams to heat and air leaking into the attic, and NRCan’s [Keeping the Heat In](https://natural-resources.canada.ca/energy-efficiency/homes/make-your-home-more-energy-efficient/keeping-the-heat/chapter-5-roofs-and-attics/15637) includes a section on ice dams within its chapter on roofs and attics. In practice, big icicles and thick ice along the eaves after modest snow are a clue that the attic is running warm. ## How do you fix attic frost and ice dams? Seal the air leaks first, then top up insulation, then check that ventilation works. Adding vents or insulation without air sealing usually treats the symptom rather than the cause. - **Air seal the attic floor:** seal around fans, pot lights, wiring, plumbing stacks, chimney chases and the hatch. An insulation or air sealing contractor does this best. - **Fix bathroom fans:** connect each fan to an insulated duct that ends at an exterior hood, and run it during and after showers. - **Lower indoor humidity in deep cold:** use fans, check humidifier settings, and watch for heavy condensation on windows. - **Insulate:** bring attic insulation up to a sensible depth once leaks are sealed, keeping vents at the eaves clear. - **Balance ventilation:** make sure intake vents at the soffits are not blocked by insulation. NRCan’s guide says that if frost is particularly heavy, 10 mm or more, you should check that ventilation is present and not blocked. Be careful with ice on the roof. Chipping at ice dams can damage shingles, and roofs are dangerous in winter. A roofer can deal with the ice. The attic work is what stops it coming back. ## What signs should buyers look for? Many clues show up inside the house, even when the attic is hard to reach. - Water stains on ceilings, especially around light fixtures, fans and near outside walls. - Peeling paint or nail pops on upper-floor ceilings. - Heavy condensation or frost on the inside of windows in winter. - Large icicles or thick ice along the eaves, or staining on the soffits. - In the attic: frost on nails and sheathing, dark staining on the wood, damp or matted insulation, or rusty nail tips. NRCan’s guide also notes that discoloured insulation can be a sign of air leakage. Where mould is present, [Health Canada](https://www.canada.ca/en/health-canada/services/publications/healthy-living/addressing-moisture-mould-your-home.html) has guidance on cleaning it up and on when to bring in a professional. ## What should I ask the seller? Ask plainly, through your REALTOR®: - Has water ever dripped from a ceiling or light fixture after a cold snap? - Have there been ice dams, and has a roofer or insulation contractor done any work? - Were bathroom fans or attic insulation replaced, and is there paperwork? - Has the roof or roof sheathing been repaired for water damage? For a newer home, ask whether a warranty claim has been made. Alberta’s [new home warranty](https://www.alberta.ca/new-home-warranty-overview) includes building envelope coverage for a set number of years, and our post on [new home inspections and warranty](https://edmontonhomeinspector.com/blog/new-home-inspection-alberta-warranty) explains how claims work. ## When is the best time to check for attic frost? During or just after a long cold spell. NRCan suggests checking for frost during or right after a cold snap, when it is easiest to see. In spring or summer you look for the after-effects instead: staining, rusty nails and damp or flattened insulation. If you are buying in summer, the report may show only old stains. That is still useful, but a follow-up look the next winter is a good habit. Our [home inspection checklist](https://edmontonhomeinspector.com/resources/home-inspection-checklist) is handy for both. A [pre-purchase inspection](https://edmontonhomeinspector.com/services/pre-purchase-home-inspection) includes the attic where it can be entered safely, and you can [join the priority list](https://edmontonhomeinspector.com/book) when you are ready. ## Sources - [Keeping The Heat In - Section 5: Roofs and attics](https://natural-resources.canada.ca/energy-efficiency/homes/make-your-home-more-energy-efficient/keeping-the-heat/chapter-5-roofs-and-attics/15637), Natural Resources Canada - [About your house: Attic venting, attic moisture, and ice dams](https://publications.gc.ca/site/eng/9.615641/publication.html), Canada Mortgage and Housing Corporation - [Managing attic rain](https://www.travelerscanada.ca/resources/home-warranty/managing-attic-rain), Travelers Canada - [‘Attic rain’ could plague more Alberta homes this winter](https://amp.cbc.ca/lite/story/1.3933782), CBC News - [Attic rain in Calgary and Alberta cold weather](https://www.cbc.ca/news/canada/calgary/attic-rain-calgary-alberta-cold-weather-1.7097529), CBC News - [Guide to addressing moisture and mould indoors](https://www.canada.ca/en/health-canada/services/publications/healthy-living/addressing-moisture-mould-your-home.html), Health Canada - [New home warranty – Overview](https://www.alberta.ca/new-home-warranty-overview), Government of Alberta ## Questions readers ask ### Is a little frost in the attic normal in an Edmonton winter? A light dusting during a deep cold spell can happen. NRCan suggests checking ventilation and air leaks if the buildup is heavy, around 10 mm or more. ### Will adding more roof vents fix attic frost? Usually not on its own. Most attic moisture comes from house air leaking in, so sealing those leaks and venting bathroom fans outside comes first. ### Why does my ceiling drip after a cold snap ends? Frost that built up on the attic side of the roof during the cold melts quickly when temperatures rise, and the water drips onto the ceiling and through fixtures. This is often called attic rain.